Inhlaled Anesth. Part 2 Add-On Flashcards
Most drugs will decrease MAC requirement with the exception of:
Acute amphetamine, cocaine, ephedrine
Chronic ampthetamine use will decrease MAC
_____% of patients should not move at 1.2 MAC.
95%
MAC has a standard deviation of ~ 10%
T/F all the drugs at 1 MAC are equal, it just takes more drug to get to MAC.
True
What is MAC awake?
- the minimum concentration where 50% of people respond to the command “open your eyes”
- this end tidal concentration is 1/3 MAC
- associated with loss of recall
What is MAC bar?
MAC necessary to block adrenergic response to skin incision
~ 1.5 MAC
- changes in norepinephrine concentration: HR, MAP
What is MAC intubation?
Similar to MAC bar
- it’s value exceeds the anesthetic requirement for skin incision
MAC is additive. What restricts this?
Amount of time between doses of muscle relaxants—> pt won’t move, but it doesn’t mean they don’t want to
What is elimination like with volatile anesthetics?
They are exhaled unchanged, or minimally metabolized by the liver
What is the primary objective with inhaled anesthetics?
To obtain a constant and optimal partial pressure (Pbr) of anesthetic in the brain
- do this by controlling inspired partial pressure of gas
- the brain and all other tissues equillibrate with the partial pressure of anesthetic delivered to them by arterial blood
Transfer from blood to brain depends on:
- brain:blood partition coefficient (1.7, 1.57, 1.39)
- cerebral blood flow
- arterial/venous partial pressure difference
How does the rate of breathing (hyper vs hypoventilation) affect induction?
- hyperventilation increases induction
- hypoventilation slows induction
- spontaneous ventilation is always better —> pulls gas instead of you pushing it in
What do you do if the surgeon is ready for incision, but the patient is not?
Turn up the concentration and flows to hurry up and get them where you want the to be
** RATE OF GAS FLOW IS VERY IMPORTANT **
What are the implications of high blood solubility?
A large amount of anesthetic must be dissolved in blood before equilibrium with gas phase is reached
What does high CO (fear) do for induction?
Slows induction (rate of rise is slower) - blood moving so fast you can’t fill up all of the seats
What does low CO (shock) do for induction?
Speeds up induction (speeds up rate of rise)
- blood moving slower, more time to fill up seats
What will a right to left shunt do to the rate of induction and what is this called?
Slows rate of induction—> “dilutional effect”
Bypasses the lungs
How many time constants are required for complete equilibration of any tissue, including the brain, with the Pa?
How long is this in minutes?
At least 3 time constants
6-12 min
What does PA-PV reflect?
The tissue uptake of inhaled anesthetic
After 3 time constants,how much of returning venous blood flow is at the Sam partial pressure as PA?
75%
- as end tidal concentrations increase we know tissues are getting more saturated with agent
Emergence is the inverse of induction. What 3 factors play into this?
- alveolar ventilation—>use high FGF and hyperventilate to wash out gas
- solubility
- CO
During emergence, there is a potential for “diffusion hypoxia”. What does this mean?
Happens when nitrous oxide is abruptly stopped, and pp in blood is higher than in alveoli
(Nitrous diffuses faster than oxygen)
When nitrous stopped, it diffuses rapidly into the alveoli, diluting O2 concentration—> hypoxia
* prevent this by giving 100% O2 for 5-10 minutes after N2O stopped *
What are factors that influence the rates of emergence?
- duration of procedure—> how long gas was running
- temperature of patient: cooler pt=gas more soluble, slower emergence
- physical condition of patient—> not doing well will slow things down
- obesity: may initially wake up, bu then as agent is mobilized from fat stores they may re-anesthetize themsleves
How much anesthetic must be eliminated for pt to regain coordinated functions?
All but a small amount to restore the ability to swallow and maintain effective respiratory effort
